Indoor positioning services refers to methods where networks of devices and algorithms are used to locate mobile devices within buildings. Indoor positioning is regarded as a key component of location-aware mobile computing and is a critical element in providing augmented reality (AR) services, Location-aware computing refers to applications that utilize a user's location to provide content relevant to that location. Additionally, AR is a technology that overlays a virtual space onto a real (physical) space. To successfully enable AR and location-aware computing, accurate indoor positioning is a key requirement.
Global Positioning Systems (GPS) loses significant power when passing through construction materials, and suffers from multi-path propagation effects that make it unsuitable for indoor environments. Techniques based on received signal strength indication (RSSI) from WiFi and Bluetooth wireless access points have also been explored. However, complex indoor environments cause radio waves to propagate in dynamic and unpredictable ways, limiting the accuracy of positioning systems based on RSSI. Ultrasonic techniques (US), which transmit acoustic waves to microphones, are another method which can be used to approximate indoor position. They operate at lower frequencies than systems based on WiFi and attenuate significantly when passing through walls. This potentially makes US techniques more accurate than WiFi or Bluetooth techniques.
Optical indoor positioning techniques use optical signals, either visible or infrared, and can be used to accurately locate mobile devices indoors. These are more accurate than the approaches mentioned previously, since optical signals are highly directional and cannot penetrate solid objects. However this directionality limits the potential reliability of optical signals, since difficulty in aligning the receiver and transmitter can occur.